Ebola is a rare, often deadly virus that causes a severe illness called hemorrhagic fever. Infection with the virus can damage blood vessels, affect multiple organs (e.g., kidneys, liver), and often leads to excessive bleeding (hemorrhage).

Ebola spreads through direct contact with the blood or body fluids of a person who has an Ebola infection or of someone who has died from it. A person is contagious only after symptoms appear. Contaminated objects such as needles can also transmit Ebola, as can contact with infected wildlife. Ebola enters the body through mucous membranes like the eyes and nose or broken skin. The virus does not spread through air, water, or casual contact with a carrier.

The Ebola virus incubates for about 8 to 10 days before moving to lymph nodes, then the liver, spleen and adrenal glands. Early Ebola symptoms are flu-like and similar to more common diseases like malaria and meningitis. Later symptoms become more severe and include unexplained bleeding and organ failure.

According to the World Health Organization (WHO), the Ebola fatality rate has ranged from 25% to 90%, depending on the outbreak.

In 1976, scientists first identified Ebola in what is now the Democratic Republic of the Congo. Since then, sub-Saharan Africa has been affected by periodic Ebola outbreaks. The West African outbreak that began in 2014 and ended in 2016 was the largest ever recorded, with 15,261 laboratory-confirmed cases, according to the WHO.

During that outbreak, ten people with Ebola were treated in the U.S. Two acquired it in the U.S. and the other cases were acquired in West Africa.

Since Ebola requires direct contact to spread from person-to-person, the risk of an outbreak in the U.S. is very low. Patients are not routinely tested for Ebola. A person may be tested if that person recently visited an area where the virus was reported and have symptoms, or if someone knows that he or she has been exposed to the virus and have symptoms consistent with an Ebola infection.

In addition to Ebola, other viruses causing hemorrhagic fever include Marburg, Hantavirus, and yellow fever. Many hemorrhagic fever viruses rely on an animal or insect host to survive. In the case of Ebola, these hosts are likely bats. Apes and monkeys can carry the virus too. Hemorrhagic fever outbreaks tend to be restricted to regions where those hosts live. Sometimes travelers carry the viruses outside the regions where the outbreak originated.

Early Ebola symptoms are usually non-specific and often similar to other infectious diseases that cause a high fever, and it can be difficult to distinguish between the diseases. If a healthcare practitioner suspects someone has a hemorrhagic fever, or a disease with similar symptoms, specific diagnostic tests will be used to identify the virus or bacteria.

Individuals being tested for the Ebola virus need to be isolated. Healthcare providers and anyone who may come into contact with the patient's blood and body fluids, including laboratory personnel, need to take extra safety precautions. Local and national public health officials are also notified if Ebola is suspected.

Since Ebola cases are extremely rare in the U.S., someone will not be tested for the virus unless that person has symptoms of Ebola plus one risk factor for infection, such as a history of being near an Ebola outbreak or contact with an infected person.

The Centers for Disease Control and Prevention (CDC) provides guidance for determining if someone has a risk factor that should trigger Ebola testing. For example, unprotected contact with someone who has the virus is a high-risk activity. Traveling to a country where Ebola transmission is widespread in urban areas but with no known exposures to infected individuals is considered a low-risk activity.

Individuals may be tested for other diseases with similar symptoms, including malaria, typhoid fever, Marburg virus and other hemorrhagic fevers, plus bacterial infections like pneumonia. The CDC points out that consideration of Ebola should not delay testing, diagnosis, and care for other more likely conditions.

There is no test available to detect Ebola before symptoms begin. It can take up to three days after the start of symptoms to detect the virus, so some individuals may need to be tested more than once to avoid false-negative results.

RT-PCR of blood is now the standard method used by international health organizations to diagnose acute Ebola during outbreaks. Saliva testing is the standard for postmortem testing. However, the laboratory infrastructure and staff training required for molecular testing still makes it challenging to deploy in resource-limited areas.

Ebola antigen tests—these tests detect Ebola antigens in blood samples. They typically can detect antigens within a few days after symptoms (e.g., fever) begin. Two types are available:

Rapid Ebola antigen tests—these tests are designed to be performed at the point of care (e.g., near the patient) using a finger stick blood sample, providing results in under an hour. They also detect viral antigens in saliva postmortem. Rapid tests emerged during the 2014 West African outbreak and research continues on the best role for them in the future.

Laboratory antigen tests—these tests also detect Ebola antigen in blood samples but are designed to be performed in laboratories by laboratory personnel.

Ebola antibody testing, IgM or IgG class—these tests are used to detect Ebola antibodies (immune proteins) in a blood sample that develop in response to the infection. The IgM class of antibody develops first, while IgG develops later. Antibody tests in general are best at detecting Ebola later in the illness and are often used in investigating Ebola outbreaks.

The World Health Organization (WHO) and the CDC recommend molecular testing and antigen ELISA testing for diagnosing acute Ebola.

The WHO recommends initial testing with a rapid point-of-care test when there is no molecular testing available for triage during an outbreak.

In the U.S., public health laboratories are responsible for laboratory testing for Ebola. If a hospital chooses to use a rapid point-of-care test, it must still submit samples to a public health laboratory for confirmatory testing.

In research settings, Ebola viral cultures may be used to detect the virus in tissue samples. However, these tests require a high containment biosafety level 4 laboratory usually found only at specifically approved research and national public health laboratories, so they are not commonly used for Ebola testing.

Other tests

Laboratory tests may be used to establish and monitor the disease's impact on body function. Examples of these tests may include:

There is no FDA-approved Ebola vaccine. Researchers are currently studying candidate vaccines.

Ebola prevention is of greatest concern for people traveling to regions affected by outbreaks and for healthcare and laboratory workers.

Individuals traveling to countries experiencing Ebola outbreaks should wash or sanitize their hands frequently and generally avoid contact with sick people and the deceased. The Centers for Disease Control (CDC)'s website provides further details about Ebola prevention for travelers.

Healthcare workers, including laboratory workers, need to follow specific safety procedures during an Ebola outbreak. According to the CDC, examples of these include:

Avoiding direct contact with the bodies of people who have died from Ebola

Notifying health officials in case of direct contact with the blood or body fluids of someone sick from Ebola

To protect the blood supply in the U.S., there are several new recommendations from the Food and Drug Administration (FDA) for people wishing to donate blood. People with a history of Ebola virus infection are deferred indefinitely. Individuals with possible exposure to Ebola are deferred from donating blood for 8 weeks. This includes, for example, people who have lived in or traveled to a country with widespread Ebola transmission and those who have had close contact with any body fluids (e.g., blood, urine, saliva, vomit) of a person who has or may have Ebola virus infection. For more information, see the AABB webpage Blood Donation Information.

Treatment

There are no licensed therapeutics to treat Ebola, though researchers are evaluating potential immune therapies, blood products, and drugs.

(Updated 2015 May 28). Epidemiologic risk factors to consider when evaluating a person for exposure to Ebola virus. Centers for Disease Control. Available online at https://www.cdc.gov/vhf/ebola/exposure/risk-factors-when-evaluating-person-for-exposure.html. Accessed February 8, 2017.

(Updated 2015 October 8). Guidance for U.S. laboratories for managing and testing routine clinical specimens where there is a concern about Ebola virus disease. Centers for Disease Control. Available online at https://www.cdc.gov/vhf/ebola/healthcare-us/laboratories/safe-specimen-management.html#two. Accessed February 8, 2017.